Community- and Healthcare-Associated Methicillin-Resistant Staphylococcus aureus Strains: An Investigation Into Household Transmission, Risk Factors, and Environmental Contamination.

Abstract

OBJECTIVE To measure transmission frequencies and risk factors for household acquisition of community-associated and healthcare-associated (HA-) methicillin-resistant Staphylococcus aureus (MRSA). DESIGN Prospective cohort study from October 4, 2008, through December 3, 2012. SETTING Seven acute care hospitals in or near Toronto, Canada. PARTICIPANTS Total of 99 MRSA-colonized or MRSA-infected case patients and 183 household contacts. METHODS Baseline interviews were conducted, and surveillance cultures were collected monthly for 3 months from household members, pets, and 8 prespecified high-use environmental locations. Isolates underwent pulsed-field gel electrophoresis and staphylococcal cassette chromosome mec typing. RESULTS Overall, of 183 household contacts 89 (49%) were MRSA colonized, with 56 (31%) detected at baseline. MRSA transmission from index case to contacts negative at baseline occurred in 27 (40%) of 68 followed-up households. Strains were identical within households. The transmission risk for HA-MRSA was 39% compared with 40% (P=.95) for community-associated MRSA. HA-MRSA index cases were more likely to be older and not practice infection control measures (P=.002-.03). Household acquisition risk factors included requiring assistance and sharing bath towels (P=.001-.03). Environmental contamination was identified in 78 (79%) of 99 households and was more common in HA-MRSA households. CONCLUSION Household transmission of community-associated and HA-MRSA strains was common and the difference in transmission risk was not statistically significant. Infect Control Hosp Epidemiol 2016;1-7.